The present invention relates to a device for pressurizing a liquid by means of an electrostrictive vibrator and, more particularly, to a pump furnished with an electrostrictive vibrator which is suitable for pressurizing a small volume of liquid such as ink to be supplied to a head of an ink jet printer.
A liquid pressurizing pump of the type described usually includes a pump housing, a suction valve and a delivery valve which are located respectively in a suction port and a delivery port formed in the pump housing, a liquid chamber communicating to the suction port and delivery port, and an electrostrictive vibrator adhered to part of the walls of the pump housing or the outer surface of a closure plate for closing the liquid chamber, which commonly constitutes a vibration plate. An AC voltage is applied to the electrostrictive vibrator to cause it into displacement so that the vibration plate integral with the vibrator is bent relative to the liquid chamber to vary the volume of the chamber. A liquid is sucked into the liquid chamber via the suction valve in response to the change of the volume of the chamber and the pressurized liquid is fed out via the delivery valve.
The liquid pressurizing pump constructed as described above is capable of causing the vibration plate to undergo a substantial bend in response to a relatively small displacement of the electrostrictive vibrator, thereby developing a substantial change in the volume of the liquid chamber. However, the problem with such a pump is that while the energy consumed for bending the vibration plate, i.e. the force acting in parallel to the vibration plate, is large, the energy for delivering the liquid, i.e. the force acting perpendicular to the vibration plate, is small, limiting the available pressure for the delivery of the liquid.
Meanwhile, the AC voltage applied to the vibrator of the prior art pump usually appears in a train of pulses and, for this reason, the vibration of the vibrator is sharp. Therefore, and particularly because the vacuum generated in the event of suction is strong, air bubbles tend to be formed in the liquid.